An image-sensor device is one of the building blocks in a digital imaging system such as a digital still or a video camera. An image-sensor device includes a pixel array (or grid) for detecting light and recording intensity (brightness) of the detected light. The pixel array responds to the light by accumulating a charge—for example, the more light, the higher the charge. The accumulated charge is then used (for example, by other circuitry) to provide a color and brightness signal for use in a suitable application, such as a digital camera. One type of image sensor is a backside illuminated (BSI) image sensor device. BSI image sensor devices are used for sensing a volume of light projected towards a backside surface of a substrate (which supports the image sensor circuitry of the BSI image sensor device). The pixel grid is located at a front side of the substrate, and the substrate is thin enough so that light projected towards the backside of the substrate can reach the pixel grid. BSI image sensor devices provide a reduced destructive interference, as compared to front-side illuminated (FSI) image sensor device.
Integrated circuit (IC) technologies are constantly being improved. Such improvements frequently involve scaling down device geometries to achieve lower fabrication costs, higher device integration density, higher speeds, and better performance. Along with the advantages realized from reducing geometry size, improvements are being directly to the IC devices. One such IC device is an image sensor device.
Due to device scaling, improvements to BSI technology are continually being made to further improve the quality of BSI image sensor devices. Although existing BSI image-sensor devices and methods of fabricating BSI image sensor devices have been generally adequate for their intended purposes, as device scaling-down continues, they have not been entirely satisfactory in all respects.